The invention relates to servo drivers for motor vehicles.
Servo drivers for motor vehicles comprise an electromechanical (more particularly electromagneto-mechanical) energy converter having a rotatably mounted disc rotor for generating torque; a stepping up mechanism connected on the output side of the disc or rotor for coupling the disc rotor to an output element while simultaneously stepping up (more particularly in the form of a so-called reduction) of the torque acting on the disc rotor; as well as a locking mechanism which under the action of torque introduced on the output side into the servo drive locks a rotational movement of the output element and prevents the transfer of torque introduced on the output side over to the drive side, i.e., to the disc rotor.
The term “disc rotor” herein means a flat armature disc whose diameter is clearly greater than the height thereof (axial extension).
“Locking” a (rotational) movement of the output element means that when torque is introduced on the output side, only a slight restricted movement of the output element is to be possible to the extent required for activating the locking mechanism, but no substantial movement of the output element beyond that. In other words, any (rotational) movement of the output element is prevented insofar as it substantially exceeds a restricted movement required for actuating or shifting (activating) the locking mechanism; more particularly the locking mechanism is to prevent the output element from being able to rotate freely (around several revolutions) under the action of torque introduced on the output side, as is the case when torque is introduced on the drive side (through the disc rotor). The energy connected with the introduction of torque on the output side is thereby taken up, for example, by the locking mechanism.
The locking mechanism need not for this engage on the output element itself but can, for example, also act on a gear element of the stepping up mechanism. Decisive is only that torque introduced on the output side is blocked at some suitable point of the servo drive so that it cannot trigger any significant adjusting movement of the elements of the servo drive (more particularly not the output element).
The stepping up mechanism can, in the limiting case, also have a transmission ratio of 1:1 and then acts purely as a coupling mechanism for transferring torque between the disc rotor and the output element; in this case it can simply be formed by coupling elements mounted on the disc rotor (more particularly on its periphery) which act to transfer force or torque to the output element.
By introducing torque into the servo drive “on the output side” is meant introducing torque through an element which is mounted on the output side of the output element, thus which (seen from the drive side, i.e., from the disc rotor) lies in the force or torque flow behind the output element, such as e.g., a cable drum which as a constituent part of an adjusting mechanism of a window lifter is mounted behind the output element and is driven through same.
Servo drives are particularly suitable for adjusting adjustable parts in motor vehicles. For this the corresponding adjusting part of the motor vehicle is coupled to the output element of the servo drive. When using the servo drive in a vehicle window lifter for raising and lowering a window pane the output element of the servo drive can be connected, by way of example, to a cable drum about which is looped the drive cable which acts as the draw means for the vehicle window lifter. The servo drive then serves to generate a rotational movement of the cable drum connected to the output element and which in turn causes a movement of the drive cable which serves as the draw means through which the window pane is raised and lowered for adjustment.
By using a so-called disc rotor, i.e. an armature disc in the electromechanical energy converter, which on the basis of the electro-motorized principle provides the torque required for actuating the output element, a flat construction of the servo drive is sought corresponding to the small space which is normally available in motor vehicle doors for housing the servo drive. By means of the stepping up mechanism provided between the disc rotor and the output element, particularly when using the servo drive for adjusting adjustable parts in motor vehicles, a so-called reduction thereby takes place, i.e., the output element rotates at a lower speed than the disc rotor and consequently provides a greater torque for adjusting the corresponding adjustable part, such as e.g., a window pane.
With adjusting systems of this kind it is of great importance that torque introduced on the output side is not transferred to the drive side or leads to no substantial rotational movement on the output element. Thus, for example, it is to be prevented that a window pane of a motor vehicle can be lowered if a sufficiently large force is exerted on the window pane itself. If the transfer of such torque introduced on the output side to the drive side of the servo drive is not prevented, then the window pane could be lowered by forces applied to the window pane itself whereby the disc rotor would rotate along a direction which corresponds to a lowering of the window pane.
It is known to prevent such a return action of adjusting forces applied on the output side to the drive side through a self-locking design of the drive system. This has the drawback, however, that the efficiency of the servo drive is reduced.
A further possibility lies in using additional locking mechanisms which when introducing torque on the output side into the servo drive are activated and hereby act on an element of the servo drive so that the latter is locked and transfer of torque to the drive side is prevented. However the problem here is that the additional locking mechanisms take up additional space and therefore stand in the way of the smallest possible compact construction of the servo drive in the axial direction.